Understanding the sensitivity of reference evapotranspiration (ET0) to meteorological variables is critical for improving urban water management and climate adaptation strategies. This study analyses the one-way and two-way sensitivity of ET0 to maximum temperature (Tmax), wind speed (u2), net solar radiation (Rn), and maximum relative humidity (RHmax) using the FAO-56 Penman-Monteith equation for multiple meteorological stations in Paris area. One-way sensitivity analysis revealed that Tmax and Rn have the strongest influence on ET0 in summer, while wind speed and RHmax show secondary but notable effects, particularly in winter and transitional seasons. A two-way sensitivity analysis was conducted for Tmax and RHmax, considering their joint influence on vapor pressure deficit (VPD). The results indicate a nonlinear relationship, where higher Tmax and lower RHmax significantly increase VPD, amplifying ET0, while increasing RHmax dampens this effect. Seasonal variations highlight stronger ET0 sensitivity in summer and reduced impact of Rn in winter due to high humidity levels. Windspeed has its major role in shaping evapotranspiration in winter and in dense urban settings. These findings emphasize the need for climate-adaptive urban drainage models, integrating ET0 variability to enhance stormwater retention, flood resilience, and green infrastructure efficiency under changing climate conditions. Future research should refine ET0 modelling for urban microclimates, ensuring accurate water balance predictions in cities
